1. Field of the Invention
This invention relates to a semiconductor device and its manufacturing method, particularly to a compound semiconductor device such as a hetero-junction bipolar transistor (HBT) and a high electron mobility transistor (HEMT).
2. Description of the Related Art
Indium gallium phosphide (InGaP) comes to be used as part of laminated films in recent compound semiconductor devices. Indium gallium phosphide is expected to become a film which replaces aluminum gallium arsenide (AlGaAs) because its reliability in being connected with gallium arsenide can be increased since its lattice constant can be set to be the same as that of gallium arsenide (GaAs), and its characteristic is excellent.
The characteristic of indium gallium phosphide is excellent because of the factors that a deep level called DX center is not formed when indium gallium phosphide is doped with silicon (Si) and that oxygen is hard to be taken in as impurities since it does not include aluminum (Al).
As the compound semiconductor devices using indium gallium phosphide, a HEMT which uses indium gallium phosphide as an electron supplying layer and an HBT which uses indium gallium phosphide as an emitter layer are known.
When indium gallium phosphide is used in the compound semiconductor devices, it is necessary to form layers including arsenide (As) such as gallium arsenide on its upper and lower layers, but it is reported that abnormalities occur under this circumstances at an interface between the layers including indium gallium phosphide and arsenide such as gallium arsenide. The abnormalities are the phenomenon that a carrier is depleted when gallium arsenide is formed on indium gallium phosphide and that carriers are accumulated when indium gallium phosphide is formed on gallium arsenide. This happens when a natural superlattice is formed on indium gallium phosphide. When gallium arsenide without the natural superlattice is formed on indium gallium phosphide with the natural superlattice formed thereon, a distortion occurs at the interface, which causes these abnormalities to occur.
FIG. 1 is a graph showing a carrier density (an n-type electron density) when a gallium arsenide film is formed on an indium gallium phosphide film, in which the axis of ordinates shows the carrier density and the axis of abscissas shows the depth from the surface of the gallium arsenide film. The alternate long and short dash line II-IIxe2x80x2 shows the position of the interface between the indium gallium phosphide film and the gallium arsenide film. Thus, when the indium gallium phosphide film and the gallium arsenide film are connected, there arises a problem that the carrier is depleted near the interface.
As a result, an electrical resistance is increased when the carrier passes through the interface, which brings about problems such as an ohmic defect, an increased on-resistance, and a Gm dispersion, when the indium gallium phosphide film is used in the HEMT. Further, there arises a problem such as an increase of an emitter resistance when the indium gallium phosphide film is used in the HBT.
It is an object of the present invention to provide a semiconductor device with increased reliability and its manufacturing method, which is for a compound semiconductor device using an arsenical grown film such as a gallium arsenide film, by preventing carrier depletion near the connecting surface of a thin film which is connected to the grown film.
A semiconductor device according to the present invention comprises an arsenical grown film provided in laminated films, and a thin film directly connected to the grown film. The thin film is an indium gallium phosphide film containing antimony.
Preferably, the thin film forms part of an electron supplying layer of a high electron mobility transistor.
Preferably, the density of antimony in the thin film is within the range of 5xc3x971017cmxe2x88x923 to 5xc3x971020cmxe2x88x923.
Preferably, the thin film forms part of the emitter layer of a hetero-junction bipolar transistor.
Alternatively, the thin film may form part of the collector layer of the hetero-junction bipolar transistor.
Preferably, the thin film has its composition expressed by InxGa(1xe2x88x92x)P(1xe2x88x92y)Sby, where x is within the range of 0.3 to 0.7.
Preferably, the thin film contains aluminum.
Preferably, the thin film is made up from two or more layers, the one of which closest to the grown film contains antimony.
Preferably, the grown film is a gallium arsenide film.
Preferably, the gallium arsenide film contains aluminum.
The present invention is mainly directed to a case wherein the thin film has a natural superlattice structure.
A manufacturing method of the semiconductor device according to the present invention comprises the first step of forming an indium gallium phosphide film containing antimony on a semiconductor substrate, and the second step of forming an arsenical grown film on the indium gallium phosphide film.
Preferably, the grown film is a gallium arsenide film.
Preferably, in the second step, aluminum is introduced into the gallium arsenide film.
The present invention comprises the above-described technical means, thereby deterring a density of n-type impurities from decreasing at the interface between the arsenical grown film such as a gallium arsenide film and the thin film by antimony included in the thin film which is connected to the grown film. As a result, an electrical connection between the grown film and the thin film can be excellently secured and a reduction of an on-resistance can be achieved without preventing electrons from moving at the interface.
According to the present invention, in the compound semiconductor device using an arsenical grown film such as a gallium arsenide film, the carrier can be deterred from depleting near the connecting surface of the grown film with another film. Therefore, it is possible to increase the characteristic of the device, as well as to provide the semiconductor device and its manufacturing method, which achieves the low manufacturing cost.